The present invention concerns an exhaust gas particle filter for internal combustion engines.
The conventional homogeneously constructed exhaust gas particle filters require fine porosity so that the specified total degree of separation can be sufficiently large.
Because of the fine porosity and the small probability or regeneration, choking of the filter is, in the long term, unavoidable. In order to keep the pressure drop caused by the choking of the filter within acceptable limits, a large filter surface is provided. This inevitably involves a large filter mass and, since fine porosity implies almost complete heat exchange, a large time constant. If an exhaust gas particle filter located on the high pressure side is provided for supercharged internal combustion engines, between 10 and 20 seconds generally pass after a cold start before the supercharge pressure has built up.
Although this disadvantage can be mitigated by reducing the volume of the filter, this measure itself leads to unacceptably rapid choking of the filter, which would then cause an increase in back pressure. Increasing the porosity does not produce the desired improvement either because this measure reduces the degree of separation, on the one hand, and must involve an inadequate remedy with respect to the heat storage, on the other.
In supercharged internal combustion engines, it is known practice to pass part of the exhaust gases, over a certain power range of the engine, through a bypass directly in front of the supercharger. If the bypass comes into operation during the acceleration phase, the soot generation is, of course, higher for this period (which is characterised by a heavy load) than it is during the rest of the operation. However, the legal limits are not exceeded overall--despite the unfiltered proportion--because a passenger car in normal operation is only accelerating for a small percentage of the time. An objectional feature of this possibility is that the system can be misused by jamming it in the bypass position and so contradicting the legislative intention. It follows that appropriate safety measures should come into action when the bypass control fails.
It is on this point that the invention is intended to provide a remedy. An objective of the invention, is to achieve specific filtration of the exhaust gases during the whole of the operation, using an exhaust gas particle filter of the type mentioned at the beginning. Another objective of the invention is to remove the heat sink property of the exhaust gas particle filter as far as possible, so that the downstream supercharger can respond rapidly. A further objective of the invention is to make possible the combustion of the soot which has been filtered out, so as to provide continuous regeneration of the exhaust gas particle filter.